The present invention relates to a piezoelectric element having a piezoelectric layer, and also to an actuator and an inkjet head using a piezoelectric element.
Piezoelectric members have been used in various devices for various purposes in the prior art. Examples of such devices include an actuator for producing a displacement according to a voltage applied to the piezoelectric member, and an acceleration sensor or an angular velocity sensor for producing a voltage from a displacement of the piezoelectric member.
A commonly used piezoelectric material is a lead-based dielectric material having a good piezoelectric characteristic, particularly, a perovskite-type ferroelectric material having a composition of Pb(Zr1−xTix)O3 (abbreviated as “PZT”). In the prior art, a piezoelectric element is produced by shaping a sinter of a piezoelectric material (which has been obtained through a heat treatment) through a cutting process, a polishing process, etc., into a piezoelectric layer having a shape that is suitable for the intended purpose, and then providing a pair of electrodes on the two opposing surfaces of the piezoelectric layer.
In recent years, researches have been made in the art for reducing the size of various devices using the piezoelectric element, enhancing the functionality thereof, and reducing the power consumption thereof (reducing the driving voltage), so that the various devices can be used in micro-machines, micro-sensors, or the like. It is expected that this will enable a minute and precise control, etc., in various fields in which such a control has not been expected to be possible.
In view of this, aside from conventional manufacturing methods that use a sintering process, a cutting process, a polishing process, etc., researches have been made in the art for developing a subminiature piezoelectric element having a higher precision, by using minute process techniques that have been used in semiconductor processes, or the like, on a thin piezoelectric film formed on a substrate. However, in reducing the size of a piezoelectric element, there are many problems left to be solved, including how to cause, and detect, a minute displacement in a piezoelectric film with a high precision and a high efficiency.
Now, the process of forming a piezoelectric film on a substrate (thin film process), which is superior in terms of minuteness, precision, functionality and workability, is performed in a completely different way from the minute shaping process using a sinter, which has been used in the prior art. Therefore, it is necessary to realize a structure for a piezoelectric member and a piezoelectric element that is suitable for the thin film process. Commonly used methods for producing thin piezoelectric film having a good voltage characteristic include a CVD method, a sputtering method, and a sol-gel method. With these methods, it is difficult to obtain a good characteristic unless a thin PZT film is epitaxially grown using a single crystal substrate such as an MgO single crystal substrate or an SrTiO3 single crystal substrate. Moreover, in order to stably obtain a piezoelectric characteristic, it is necessary to deposit a piezoelectric film of (Pb,La)TiO3, PbTiO2, or the like, on a single crystal substrate. An MgO single crystal substrate, an SrTiO3 single crystal substrate, and the like, have been used as the single crystal substrate.
However, substrates such as an MgO single crystal substrate and an SrTiO3 single crystal substrate are very expensive and have a size of about 30 mm×30 mm. Thus, such a substrate of a large area cannot be obtained. On the other hand, there are no techniques established in the art for forming a piezoelectric film of a good piezoelectric characteristic on a substrate other than a single crystal substrate.